I'm anyone but someone to defend SLS, but this report seems rather flimsy. It seems that they're calling anything that NASA does in-house "overhead". That's not really a fair measure. A rocket is not just its physical construction; there's a huge amount of cost in research, design, testing, and support infrastructure - in the case of SLS, particularly the Exploration Ground Systems (EGS). Part of the problem however is that every time NASA builds something new, they're rarely allowed to shut it down. Including major projects with contractors. Congress keeps mandating this inefficiency, when what NASA really needs is the freedom to put large amounts of infrastructure to the axe when it can't contribute toward competitive costs, and reallocate the funds as is needed. So long as they face mandates to keep everything open (both internal, and with specific production lines run by particular suppliers), they shouldn't be criticized for their high costs - congress should.
I really think NASA would fare better if it went back more to the NACA model - a research and support organization for other players, maintaining the common infrastructure and R&D used by others - with the addition of a scientific exploration program. NASA shouldn't be making anything that a private business case can be built for (for example, rockets reaching LEO / GEO), but they should be running the DSN, range support, creating a market for private industry to continually expand/improve its capabilities, nurturing startups to increase competition, and extensively working to bring more advanced technologies (that the market couldn't afford to sink money into due to the risk) from theory into real world - not trying to make "workhorses", but proof-of-concept systems that others will run with if merit and maturity can be demonstrated.
If there's a business model for it: private industry
If it's too risky or long-term for business: NASA proof-of-concept
If its a common need for multiple businesses in the field: NASA permanent infrastructure